Short path fractionating centrifugal still



1111952 I G. BURROWS 2,617,760

SHORT PATH FRACTIONATING CENTRIFUGAL STILLS Filed Dec. 10, 1948 'INVEN' I'OR M TTORNEYS Patent ecl Nov. 11, 1952 SHORT mm FRACTIONATING CEN- TRIFUGAL STILL Godfrey Burrows, Sale, England, assignor "to Metropolitan-Vickers Electrical Company Limited, London, England,

Britain a company of Great Application December 10, 1948, Serial No. 64, 576 V In England December 19, 1947 Thisinvention relates to a short path fractionating still of the centrifugal type which is adapted for operation under vacuum conditions.

A still of this general type is known in which distilland is caused to flow upwards by centrifugal action over a heated evaporating surface of inverted conical form. g

The present invention has for an object the provision of an improved form of short path fractionating centrifugal still.

A further object of the invention is to provide a centrifugal still which is particularly adapted for continuous operation with, if desired, varying degrees of reflux of the distillate.

Another object of the invention is to provide a centrifugal still in which provision isrmade for recirculating residue.

Other objects and advantages of the present inventionwill become apparent during the course of the following description of the invention with reference to the accompanying drawing, in which:

Fig. 1 is a diagrammatic sectional elevation of a centrifugal still.

Fig. 2 shows a diagrammatic fractional sectional elevation of a modification of the still of Fig. 1.

Essentially the improved still of this invention comprises a plurality of rotatable evaporating bowls arranged in an evacuable housing beneath corresponding condensing surfaces, the arrangement being such that on introducing a distilland into one bowl heavier fractions are eventually transferred to the outermost bowl and into a receiver by centrifugal action, while lighter fractions are transferred'inwardly by the condensing surfaces eventually to a central receiver.

Referring to Fig. 1, the still there shown comprises a housing I of cylindrical form in plan,

7 in which are arranged four rotatable bowls 2-5 which are separated and arranged for rotation at different speeds. Arranged above the bowls is a condenser 6 which is formed with condensing surfaces l-lO arranged over the respective bowls 2-5 and shaped so that distillate from one bowl condensing on the surface overhead drips from this surface into the next lower bowl, thus the condensate on surface Ill drips into bowl 4, that from surface 9 into bowl 3, that from surface 8 into bowl 2, whilst the condensate on surface 1 drips into a central stationary receiver II arranged on the axis of rotation of the bowls and from which distillate may be withdrawn through the pipe I2 under the control of valve l3. The condenser 6 may be formed as a casting with channels 6 for the circulation of cool- 2 Claims. (Cl. 202-205) a ing liquid and the condensing surfaces 'l-IO may be treated asby plating or polishing to facilitate wetting of the surface by the distillate.

Distilland is introduced into the housing of the still through 'pipe [4 and flows into a receiver l5 from which the overflow passes down the conical surface l6 and through a gap between the condensing surfaces I and 8'into bowl 2. Distilland thrown out of the bowl 2 by centrifugal action is deflected bythe bafiie I! into the bowl 3, and similarly the distilland thrown out of bowls 3 and 4 is deflected by baflies l8 and I9 into bowls 4 and 5 respectively. The residual distilland thrown out of bowl 5 is deflected by a bafile 20 into an annular trough 2| from which it may be withdrawn through pipe 22.

If'desired the residual distilland in the trough 2| may be recirculated through th still. For this purpose a pipe 23 is provided with valve 24 which leads from the trough 2| to a distributor 25 from which liquid flows over conical surface 26 and between gaps in the condensing surfaces 8 and 9 into bowl 3.

The bowls 2-5 are secured to respective'concentric sleeves 32-35 which are mounted on a hollow shaft 28 supported in a bearing 29 and are provided with individual gear wheels meshing with gear wheels on the lay shaft 36. It will be appreciated that by choosing the diameters of the respective gear wheels the speeds of the individual bowls may be arranged to suit required operating conditions. Each of the bowls is provided with an individual electric heater 31, the connections to which are made through the slip rings 38 so that one bowl is at a different temperature than that of another bowl.

In the operation of the still, the heavier fractions of the distilland introduced into the bowl 2 will be caused to travel outwards from bowl to bowl by centrifugal action until they reach the trough 2|. The lighter fractions however will be caused to travel inwards by the action of the condensing surfaces until they reach the receiver II. By control of the valve l3 the distillate may be caused to accumulate in the receiver and eventually to spill over into the bowl 2, and in this manner any desired degree of reflux may be obtained.

Also by control of the valve 24 any desired proportion of the residue in the trough 21 may be recirculated through the still. The controls for reflux and recirculation may be varied independently of one another and as required according to the kind and proportions of the fractions it is desired to obtain. It will be understood also that the distilland need not be fed to the bowl 2 but could, for example, be introduced into the bowl 3 so as to allow a double fractionation of the, distillate. Similarly the residue from the trough 2| may be recirculated to a bowl other than bowl 3 as shown.

In the arrangement shown in Fig. 1, the area of the condensing surface 1 may be too small for some purposes, and a modification providing a larger area is shown in Fig. 2. In this form .the central receiver H for thedistillateisofwan nular shape and connectedwith the outletvalve l3 through the channel 39 while the condensing surface 7' is formed as an annulus, which ex.- tends over the bowl 2 with its inner edge.;projecting over the outer edge of the receiver ll.

It will be appreciated that the short path fractionating still of the present invention is particularly suitable for operation under so-called molecular distillation conditions, that .is .undervacuum conditions such that-the mean free path of; the distilling molecules .in; their .passage from-the evaporator to the cendenser is of thesame order of magnitude .orgreaterthan the distance between .the evaporator and the condenser, so that the average .ldistilling, molecule travelsfrom the evaporatorto thecoiidenser substantially without collision withresidual ,gas molecules. The operation .of thest'ill =is however not necesarily confined '-to .this .type of: distillation.

What I-claim as new. an'ddesire .to tsecurelby Letters Patent Ldf .the United. States is; r

1. A .shortpath fractionating centrifugal .still comprising a plurality of concentric evaporating bowls mounted for-rotation about a-common axis, means for rotatingthe bowlsatldifferent rates of rotationrelativeto each other, meansfforiheating I-the bowls individually, .Ibaflles tfor directing liquid Iforce'd "by centrifugal action. out. of one bowl into the next outer bowl and residue out of the outermost bowl into a stationary annular channel, a plurality of concentric condensing surfaces positioned one over each bowl and shaped to feed condensate back. into the next inner bowl, a central stationary receiver for. condensate fed from the innermost condensing surface, and

means for feeding distilland to one of said bowls.

2. A short path fractionating centrifugal still comprising a plurality of concentric evaporating bowls mounted for rotation about a common axis, means for rotating the bowls at different rates, of rotation relative to each other, means for heating the bowls individually, baffies for directing liquid forced by centrifugal action out of.one bowl into the next outer bowl and residue .outof the outermost bowl into a stationary an- REFERENCES CITED The following reierencesr-areof record inthe file of this patent:

UNITED STATES Number Name Date 2,128,223 Fraser Aug. 3Q,'.1938 234.166 t'Hickman.j :Mar- '1 2,298,377 Hickman-F. ;O ct. 13,1942 "2,406,421 Wollneretal 'Augg27, 1946 

1. A SHORT PATH FRACTIONATING CENTRIFUGAL STILL COMPRISING A PLURALITY OF CONCENTRIC EVAPORATING BOWLS MOUNTED FOR ROTATION ABOUT A COMMON AXIS MEANS FOR ROTATING THE BOWLS AT DIFFERENT RATES OF ROTATION RELATIVE TO EACH OTHER,, MEANS FOR HEATING THE BOWLS INDIVIDUALLY, BAFFLES FOR DIRECTING LIQUID FORCED BY CENTRIFUGAL ACTION OUT OF ONE BOWL INTO THE NEXT OUTER BOWL AND RESIDUE OUT OF THE OUTERMOST BOWL INTO A STATIONARY ANNULAR CHANNEL, PLURALITY OF CONCENTRIC CONDENSING SURFACES POSITIONED ONE OVER EACH BOWL AND SHAPED TO FEED CONDENSATE BACK INTO THE NEXT INNER BOWL, A CENTRAL STATIONARY RECEIVER FOR CONDENSATE FED FROM THE INNERMOST CONDENSING SURFACE, AND MEANS FOR FEEDING DISTILLAND TO ONE OF SAID BOWLS. 